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- C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis. Additionally, C3b plays a role in forming a C3 convertase when bound to Factor B (C3bBb complex), or a C5 convertase when bound to C4b and C2b (C4b2b3b complex) or when an additional C3b molecule binds to the C3bBb complex (C3bBb3b complex). C3b's ability to perform these important functions derives from its ability to covalently bind to the surface of invading pathogens within an organism's body. The cleavage of C3 leaves C3b with an exposed thioester bond, allowing C3b to effectively coat and tag foreign cells by covalently binding to hydroxyl (-OH) and amine (-NH2) groups on foreign cell surfaces. This cleavage can occur via three mechanisms (classical pathway, alternative pathway and lectin pathway) that ultimately lead to the formation of a C3 convertase. Formation of a C3 convertase functions as a positive feedback loop, so as more C3b is cleaved, more C3 convertases are formed, further amplifying the signal on the surface of the microbial invader. This amplification of signal serves as a powerful tool for the immune system in effective clearance of the invading pathogen. (en)
- C3b é o maior dos dois elementos formados após a clivagem do componente do complemento 3 (C3). O C3b se liga covalentemente a superfície de células microbiais dentro do organismo. Isso leva à produção de C3-convertase ligada à superfície e, logo, mais componentes C3b (feedback positivo). O C3b ligado também auxilia na opsonização de micróbios e, logo, na fagocitose por macrófagos. O receptor do complemento 1 (CR1) em macrófagos permite a essas células a captura de micróbios recobertos com C3b. C3b auxilia também na depuração de complexos imunes (antígeno-anticorpo). C3b é clivado em C3c e C3d. (pt)
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- C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis. Additionally, C3b plays a role in forming a C3 convertase when bound to Factor B (C3bBb complex), or a C5 convertase when bound to C4b and C2b (C4b2b3b complex) or when an additional C3b molecule binds to the C3bBb complex (C3bBb3b complex). (en)
- C3b é o maior dos dois elementos formados após a clivagem do componente do complemento 3 (C3). O C3b se liga covalentemente a superfície de células microbiais dentro do organismo. Isso leva à produção de C3-convertase ligada à superfície e, logo, mais componentes C3b (feedback positivo). O C3b ligado também auxilia na opsonização de micróbios e, logo, na fagocitose por macrófagos. O receptor do complemento 1 (CR1) em macrófagos permite a essas células a captura de micróbios recobertos com C3b. C3b auxilia também na depuração de complexos imunes (antígeno-anticorpo). (pt)
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